Aggressive behavioural interactions between swans (Cygnus spp.) and other waterbirds during winter: a webcam-based study

Introduction

In January (K.L. Chang) and May 2010 (J.Y. Lei and L. Chen), we carried out two separate birding trips in the southern Zhangmu, a small town in southern Tibet (27°59′37′′N, 85°58′00′′E; 1755–2380 m a.s.l.) adjacent to Nepal. We observed birds by binoculars, made photographs and recorded sounds of some significant bird species during these trips. Among the bird species we recorded in these trips, we identified the Himalayan Black-lored Tit (Parus xanthogenys) and the Nepal Wren-Babbler (Pnoepyga immaculate) which have not been included in any checklist of birds of China (e.g. Cheng, 1987; MacKinnon et al., 2000; Zheng, 2005) and hence they are confirmed as new bird records for China. Here we describe details of these two new bird records.

Himalayan Black-lored Tit (Parus xanthogenys)

Two tits with vivid yellow facial patterns were recorded by K.L. Chang on 18 January 2010 and were quickly identified as Himalayan Black-lored Tits according to his previous birding experience of this species in Nepal (Fig. 1). In a subsequent spring trip, J.Y. Lei, L. Chen and four other observers also located and photographed a flock of Himalayan Black-lored Tits (n > 10) on the road from Zhangmu to the China-Nepal border checkpoint at an elevation of 1600 m on 12 May and 15 May 2010. This species may be either a common or an uncommon resident at Zhangmu.

Figure  1.  The Himalayan Black-lored Tit (Parus xanthogenys) (Photo by Liang Chen)

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The Himalayan Black-lored Tit (Fig. 1) is a large-sized tit, estimated to be about 13 cm in length, with a body size equally large as that of the Great Tit (Parus major) and the Yellow-cheeked Tit (P. spilonotus). It is a yellow-and-black tit, with a broad black line through the middle of its underparts, extending to the breast and throat. The long and pronounced crest, neck and front are also black with yellow cheeks. Black stripes, started from the neck, extend to the lores, constituting a striking facial pattern. The upper parts are olive-green with a few black streaks confined to the scapulars. It resembles the Yellow-cheeked Tit (P. spilonotus), probably its closest relative, as well as the other yellow-and-crested tit in the Himalayas, but this latter bird apparently lacks black in its forehead and lores. Females and young birds are reported to be duller in color than males (Grimmett et al., 1999; Rasmussen and Anderton, 2005). The flock we observed may have been a mixture of both males and female-like birds.

This species is a common resident in open tropical forests, secondary forests and edges of dense forests and groves of the Indian subcontinent, from north Pakistan through the Himalayas to eastern Nepal (Grimmett et al., 1999; Rasmussen and Anderton, 2005). Three subspecies were described under the species level, the nominate races xanthogenys, aplonotus and travancoreensis (Grimmett et al., 1999; Rasmussen and Anderton, 2005). Based on evidence of morphology and vocalization, Rasmussen and Anderton (2005) proposed that xanthogenys and the two other subspecies should be treated as two species: the Himalayan Black-lored Tit (Parus xanthogenys) (monotypic) and the India Black-lored Tit (P. aplonotus), with subspecies aplonotus and travancoreensis. Gill (2010) adopted this taxonomic treatment in the IOC World Bird Names. The location where we sighted the birds, our field description and morphological characteristics shown in the photographs, explicitly match the diagnosis of the taxon xanthogenys. Following Gill (2010), we therefore confirm that our sighting of the Himalayan Black-lored Tit (P. xanthogenys) is a new record for this bird species in China.

Nepal Wren-Babbler (Pnoepyga immaculate)

On 8 May 2010, near the Zhangmu Hotel we heard a series of high-pitched metallic notes, like "tsi-tsu-tsi-tsi-tsu-tsi-tsi-tsi", speeding up at the end and repeating several times. We then recorded its repeating sound and did play-back. The bird responded promptly and was easily lured out, standing at a fallen twig and presenting a full view to us, and was identified as a Nepal Wren-Babbler. It was a typical small, round and tailless Wren-Babbler, about 10 cm long. The bird was uniformly fulvous on its upper and under parts with dense black arrow-shaped streaks on breast and belly. Moreover, the bird did not have eye-brows.

There are three potential wren-babbler species of such a morphological type, sympatrically occurring in the Himalayas: the Scaly-breasted Wren-Babbler (Pnoepyga albiventer), the Pygmy Wren-Babbler (P. pusilla) and the Nepal Wren-Babbler (P. immaculate). Considering the species we observed at Zhangmu, we first ruled out P. pusilla by its unspotted wings and tertials (Fig. 2). We are also very familiar with the diagnostic "three-note" song by P. pusilla, which we did not hear in this case. With respect to P. albiventer, our species apparently lacks spots on its crown, mantle and wing-covers (Fig. 2). We are therefore inclined to infer that the bird is a Nepal Wren-Babbler (P. immaculate). This species is reported to have a longer and heavier bill than P. pusilla (Grimmett et al., 1999; Rasmussen and Anderton, 2005), but it was almost impossible for us, on the basis of this trait, to make detailed comparisons in these field conditions. Afterwards, we compared our derived song type to a reference song of a putative Nepal Wren-Babbler (available at http://www.xeno-canto.org/browse.php?query=Nepal+Babbler) and consolidated our preliminary judgment about the species identification. During the next few days (until 18 May), we repeatedly heard this distinctive song at many other sites between 1800–2200 m elevation around Zhangmu County, indicating that the species might be a fairly common breeder in the region.

Figure  2.  The Nepal Wren-Babbler (Pnoepyga immaculate) (Photo by Haitao Li)

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The Nepal Wren-Babbler has been neglected as a full species because its song was long thought to be a variant of the song of the Scaly-breasted Wren-Babbler (P. albiventer) (Martens and Eck, 1991). It has lately been realized that birds with this kind of song are morphologically differentiated from the Scaly-breasted Wren-Babbler (unspotted crown, mantle and wing-covers) and hence, the status of this unknown bird species was resolved. The Nepal Wren-Babbler is an endemic resident breeder of the Indian Subcontinent and the Himalayas, from eastern Nepal west to Himachal Pradesh in India. It is commonly found in temperate forests and subtropical or tropical moist montane habitats in undergrowth near streams and rivers (Grimmett et al., 1999; Rasmussen and Anderton, 2005). There are no records of this species in Tibet, China in any published checklist of birds of China, which is presumably due to wrong species identification resulting from neglect of subtle differences between this species and its close relatives.

Although Zhangmu is a small town, it has become a hot birding spot in China since it has already witnessed several new records of bird species for China in recent years, including the Himalayan Bulbuls (Pycnonotus leucogenys) (Zhang et al., 2006), Tickell's Thrush (Turdus unicolor) (Yu, 2008) and the Black-chinned Babbler (Stachyridopsis pyrrhops) (Dong and Yang, 2010). More new bird species for China are expected to be recorded at this site in the future.

Acknowledgments

We thank Yang Liu and Yat-Tung Yu for their constructive comments, which substantially improved an earlier draft. We are grateful to two anonymous reviewers who provided valuable comments on an earlier draft of this manuscript. We also thank Haitao Li, Qin Wang, Li Zhang and Jia Zhong for joining our field expeditions.